The present invention relates to a photosensitive member containing a low molecular weight organic compound.
To practice electrophotography it is generally known to introduce a direct method which comprises formation of an electrostatic latent image on the surface of the photosensitive layer of a photosensitive member by electrification and exposure, a process for making said image visible by development with a developer, and formation of copied images from said visible image which is fixed as it is directly to the photosensitive member, or a toner image transfer method which comprises transferring a visible image on a photosensitive member onto a transfer paper such as that of an ordinary paper and forming by fixing the transferred image its copied image, or a latent image transfer method which comprises transferring an electrostatic latent image from a photosensitive member onto a transfer paper and developing and fixing said electrostatic latent image on said transfer paper.
For the photoconductive material forming the photosensitive layer of a photosensitive member in the particular area of electrophotography dealt with herein, it is known that an inorganic photoconductive material such as selenium, cadmium sulfide or zinc oxide has been in conventional use in the past. Such photoconductive materials have advantages in that they may be charged to an appropriate potential in the dark, the loss of electrical charge in the dark is limited, the electric charge can be dissipated fast with irradiation of light, and so on. However, on the other hand, they have disadvantages as follows. For example, a selenium photosensitive member costs high when produced, and its inadequate resistivity to heat and mechanical impact necessitates caution in handling. A photosensitive member based on cadmium sulfide and that based on zinc oxide are not stable in sensitivity when placed in a highly humid environment and, moreover, since the colorant added as a sensitizer to them undergoes deterioration in electricification caused by corona charge and also color fading caused by exposure to light, they are lacking in stability of properties in long periods of use.
Consideration has also been given to the use of various organic photoconductive polymers, including polyvinyl carbazole. Although such polymers have advantages over the inorganic photoconductive materials in the foregoing description with respect to film forming property, lightness in weight, etc., they are inferior to the inorganic products when the sensitivity, durability and stability to change of environmental conditions are compared.
An organic photoconductive compound of low molecular weight also has an advantage in that the property of the film formed and the electrophotographic property can be controlled by adopting the right kind of the right composition ratio regarding the binder used in combination, but its combination use with a binder requires it to have a high compatibility with the binder.
A photosensitive member consisting of such an organic photoconductive compound of high or low molecular weight dispersed in a resin binder has such a defect as large residual potential and low sensitivity because of many traps for the carrier. To solve this problem it has been proposed to incorporate a charge transporting material into an organic photoconductive compound.
Many organic compounds have been named for the use as charge transporting materials, but the practice brings many problems to the fore. For example, the U.S. Pat. No. 3,189,447 described the usee of 2,5-bis(P-diethylaminophenyl)-1,3,4,-oxadiazole, whose compatibility with binders, however, is low and the material tends to separate in crystals. The U.S. Pat. No. 3,820,989 described the use of a diarylalkane derivative, which has satisfactory compatibility with binders but the repeated use causes changein sensitivity. Thy hydrazone compound in the Japanese Patnet KOKAI No. 59143/1979 is fairly satisfactory as regards the residual potential, but the use shows defects with resect to sensitivity, chargeability and the properties affected by repeated use.
It has thus been almost impractible to introduce a low molecular weight organic compound as a component of a photosensitive member to bring about a satisfactory effects.